Scientists forecast dead zone to become largest ever

Midwest floods foretell record Gulf dead zoneArea starved for oxygen could rival size of one of Great Lakes

ERIC BERGER, HOUSTON CHRONICLE

Published 5:30 am, Tuesday, June 14, 2011

Scientists predict this year's Gulf of Mexico dead zone will grow larger than any they have ever measured.

Forecasters say the dead zone will reach its maximum extent later this summer and could cover an area of about 9,400 square miles, similar in size to Lake Erie. This forecast size is more than 50 percent above the average extent during the last five years.

Ocean biologists expect such a large area zone because of record-breaking floodwaters pouring into the Gulf of Mexico from the Mississippi River this spring, delivering excess nutrients, particularly nitrogen and phosphorus. These nutrients create large algae blooms that, upon decomposition, suck oxygen out of the water.

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Fish, shrimp, crabs and other marine life in these dead zones — areas of hypoxic water - are stressed and sometimes can die due to oxygen starvation.

Last month, stream-flow rates in the Mississippi and Atchafalaya rivers leading to the Gulf were nearly twice that of normal conditions.

According to estimates from the U.S. Geological Survey, these two rivers discharged 164,000 metric tons of nitrogen into the northern Gulf in May, about 35 percent higher than average May nitrogen levels in recent decades.

That alone does not guarantee a large dead zone, however.

Strong winds and waves from hurricanes can mix the hypoxic waters into healthier parts of the Gulf, dispersing the dead zone. Or, as happened in 2009, unusual weather patterns can affect coastal winds and skew the prediction.

"Unless we have a series of storms, or unless there is a storm right before or during the cruise, we are confident," said the project's leader, Nancy Rabalais. "Many years we fear overestimating; this year we are worried that we might underestimate."

Rabalais and other scientists have documented the size of the Gulf dead zone since 1985 and have found it to have roughly doubled in size, on average, over the last quarter-century.

Last year's dead zone measured about 7,500 square miles, and although there were some predictions the BP oil spill might exacerbate the problem, scientists later found the catastrophe had no measurable effect on the area of hypoxic waters.

The dead zone that forms off the coast of Louisiana and Texas each summer has costs to commercial and recreational Gulf fisheries.